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Environment / Sustainability

Preventing the upstream migration of the New Zealand mudsnail

June 16, 2010

Waterways and aquaculture facilities throughout the western United States are at risk of invasion by the New Zealand mudsnail (Potamopyrgus antipodarum). Originally endemic to New Zealand, mudsnails were first discovered in the United States in 1987 near Hagerman, Idaho, and have since spread to all the western states, excluding New Mexico.

Stream closures, revenue losses, fish production declines

The New Zealand mudsnail is a small, freshwater snail that has spread across western North America, threatening native aquatic habitats.

The mudsnail’s high reproductive capacity allows them to reach extremely high densities in some situations (> 500,000 snails per square meter), leading to concerns that native aquatic communities and valuable sport fisheries could be negatively impacted. Several recreational fisheries have already suffered in California and Colorado by the closure of popular stretches of streams following mudsnail invasion.

Additionally, several western aquaculture facilities have been invaded by mudsnails, resulting in revenue losses associated with the costs of facility disinfection to eradicate this organism and declines in fish produced for fisheries enhancement and restoration.

Easily spread by humans

The mudsnails’ wide range of physiological tolerances and lack of effective native predators or competitors raises the possibility that it could spread to the majority of western waterways unless positive steps are taken to limit further invasion.

The New Zealand mudsnails’ rapid and wide-ranging invasion across four continents over the last 150 years can partly be attributed to the ease in which it can be inadvertently spread by humans. Mudsnails are quite small (< 6 mm at maturity) and can survive long periods of desiccation, thus allowing them to “hitchhike” between waterways on gear such as boots, waders, and rafts.

Management agencies are now working to eliminate this pathway by educating fisherman, biologists, and other recreational water users on the proper ways to disinfect gear. However, infested gear is not the only way in which mudsnails find their way into novel habitats; fish hatcheries are now being carefully monitored to ensure that their activities do not lead to further spread.

Preventing invasions is key

Because an infested aquaculture facility could easily spread mudsnails through normal stocking, it is no surprise that facilities that are found to harbor mudsnails face harsh restrictions by management agencies. In some situations, a facility may be quarantined until all of the mudsnails have been eradicated, which can be very costly in terms of both time and money and may lead to bankruptcy for some small private operations.

To protect these operations, it is important to find ways of preventing invasion in the first place. Mudsnails find their way into hatcheries in several ways, including crawling upstream through effluent pipes that connect a facility to an infested waterway. To eliminate this pathway, we need to develop a barrier system for these pipes.

Copper-based material a potential barrier

A 21.5-cm diameter PVC used to evaluate the New Zealand mudsnails' response to various copper-based materials.

One potential class of barriers is copper-based substrates such as copper sheeting or marine anti-fouling paints. Copper-based materials are commonly used to control mollusk colonization on boat hulls and other submerged structures, so there is some possibility that they could also be used in this application. To test this hypothesis, Associate Professor Christopher Myrick and Sarah Conlin conducted a pilot study in 2007-2008, in which they exposed mudsnails to several types of copper-based materials.

When compared to movements on bare PVC control surfaces, Myrick and Conlin found that the mudsnails’ crawling distance was up to seven times less on the copper surfaces, suggesting that these materials could indeed function as a barrier to mudsnails.

Variables for copper's effectiveness

Over the last several years, some at-risk hatcheries have installed these copper materials in their effluent pipes, and while in some situations they were successful, in others they were not. There could be several reasons for this difference in effectiveness, perhaps most notably—differences in the physical and chemical characteristics of each hatchery’s water supply.

It is well known that copper toxicity (and perhaps barrier efficiency) is affected by several variables including water temperature, water hardness, pH, and organic carbon concentration. The purpose of this current research is to determine the conditions under which copper-based materials function best as barriers to New Zealand mudsnails.

Experiments conducted at CSU Foothills Fisheries Laboratory

Chris Myrick, associate professor of Fish, Wildlife, and Conservation Biology, works on an experiment at the Foothills Fisheries Laboratory.

Two separate experiments were conducted to test the barrier efficiency of the following four copper-based compounds: copper sheeting (99.9 percent pure), copper mesh (99 percent pure), ablative anti-fouling paint (25 percent cuprous thiocyanate as the active ingredient), and non-ablative anti-fouling paint (39 percent cuprous oxide as the active ingredient).

All experiments were conducted at the Colorado State University Foothills Fisheries Laboratory. For the water temperature experiment, mudsnails collected from Boulder Creek (Boulder, Colo.) were acclimated to 8, 12, 18, or 24°C for a period of two weeks before the initiation of the experiment.

Copper sheet and mesh effective

In both experiments, copper sheet and copper mesh consistently reduced the crawling distance and velocity of the mudsnails, suggesting that these materials have the ability to function as effective mudsnail barriers across a broad range of temperatures and water hardness levels.

In contrast, the non-ablative anti-fouling paint did not appear to limit the mudsnails’ movement under any of the experimental conditions.

Ongoing research to determine optimal barrier

Research will continue to evaluate the performance of these copper-based compounds by testing each of them in a variety of conditions. We are currently evaluating barrier efficiency across a range of pH values.

To reduce the negative effects of copper on non-target species, we will evaluate the amount of copper that is leached from the materials. By doing so, we can determine the optimal barrier length that will block mudsnails, while also preventing unnecessary harmful effects to nearby aquatic communities.

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Excerpt from an article by Scott Hoyer, M.S. candidate, Fish, Wiildlife, and Conservation Biology. Originally published in Colorado Water, the newsletter of the Water Center of CSU, May/June 2010, Volume 27, Issue 3.